Chemiresistor sensors for detection of analytes in the fluid phase (e.g. gas and vapour) based on conductive nanocomposite materials include an electrically conductive component that is dispersed in a non-conductive or semi-conductive medium. As conductive component metal nanoparticles, carbon black nanoparticles or conductive nanofibres may be used. The non-conductive component is typically an organic material, which acts as a continuous phase in which the conductive particles are distributed. The non-conductive material may also comprise functionalized organic molecules that serve either as capping ligands for the metal nanoparticles or to interlink the particles in a three-dimensional network.
The operating principle of these sensors comprises a measurement of the change in the film resistance caused by sorption of analytes in the composite material. It is believed that the sensitivity of the chemiresistor depends on the ability of the composite material to undergo volumetric change in presence of analytes. The chemical selectivity of the chemiresistors depends to a certain degree on the chemical composition and the presence of specific functionalities in the organic component of the nanocomposite material. Typically, the detection limit to analytes of these chemiresistors lies in the low parts-per-million (ppm) concentration range.
Numerous studies have been carried out with respect to improving the sensitivity and the chemical selectivity of inorganic/organic composite chemiresistors to analytes via modification of the chemical composition of the sensitive layer [1].
In addition, a combination of a plurality of different sensors to an array will enhance the recognition capability of the device. An example for such array, which is sometimes also referred to as “e-nose” is described in [2]
[1] EP1215485 describes a method for preparation of highly selective nanoparticle/organic interlinked sensors via introducing selectivity enhancing units in the linker molecules. Introducing an additional fine tuning unit in a close proximity of the selectivity-enhancing functionality can achieve a fine-tuning of the selectivity. WO9927357 describes a sensor based on films of thiol-encapsulated Au-nanoparticles where the selectivity of the sensor is tailored by introducing functionality to the ligand shell thereby providing active sites for sorption of target analytes. U.S. Pat. No. 6,290,911 discloses a method to tune the selectivity of carbon black/polymer chemiresistors by varying the composition of the organic component using blends of polymers and/or polymer/monomer mixtures.
[2] WO9908105 discloses techniques and systems for analyte detection. Here a sensor system (e-nose) comprising a sensor array, electrical readout, a preprocessor for the electrical signals combined with pattern recognition is described in detail.
Although the achievements in tailoring the selectivity of the aforementioned composite chemiresistor sensors described above are encouraging, there is still need of improvement. Up to now the sensitivity and selectivity of the chemiresistors are enhanced by designing new organic materials with desired chemical composition and functionality. This requires extensive and complicated chemical synthetic work. The preparation of chemiresistor arrays combining different sensitive materials in one device is even more difficult and expensive because patterning steps for each individual sensitive material are involved.